A voltage supplying device for supplying source lines grouped as a plurality of source line groups with voltages has been known.
FIG. 1 is a schematic diagram showing one example of a conventional voltage supplying device 100.
The voltage supplying device 100 comprises a plurality of source line groups GS1, GS2, GS3, . . . . Each of the source line groups GS1, GS2, GS3, . . . consists of n source lines LS1 to LSn. The voltage supplying device 100 comprises a video line group GV in order to supply each of the source line groups GS1, GS2, GS3, . . . with gray scale voltages outputted from a gray scale voltage outputting means 10. The video line group GV comprises n video lines LV1 to LVn. The video line LV1 is a line for supplying a source line LS1 of each of source line groups GS1, GS2, GS3, . . . with voltages. Similarly, the other video lines LV2, . . . , LVn−1, LVn are lines for supplying source lines LS2, . . . , LSn−1, LSn of each of source line groups GS1, GS2, GS3, . . . with voltages. The voltage supplying device 100 comprises switch circuits C1, C2, C3, . . . associated with the source line groups GS1, GS2, GS3, . . . . Each of the switch circuits C1, C2, C3, . . . comprises n switching elements SW1 to SWn associated with n source lines LS1 to LSn. The voltage supplying device 100 comprises a shift register 21. The shift register 21 outputs control signals S1, S2, S3, . . . for controlling the switch circuits C1, C2, C3, . . . in synchronization with a clock signal CLK.
FIG. 2 shows a timing chart of the conventional voltage supplying device 100 shown in FIG. 1.
In the uppermost position of FIG. 2, a voltage profile on the video lines LV1 to LVn is shown every one clock period. It is noted that reference characters ‘GS1’, ‘GS2’, ‘GS3’ are described in the voltage profile. For example, the reference character ‘GS1’ is described in a period from times t1 to t2. This means that the gray scale voltages for source lines belonging to the source line group GS1 are supplied to the video lines LV1 to LVn during the period from times t1 to t2. A period from times t2 to t3 can be considered similarly to the period from times t1 to t2. The reference character ‘GS2’ is described in the period from times t2 to t3. This means that the gray scale voltages for source lines belonging to the source line group GS2 are supplied to the video lines LV1 to LVn. As described above, the video lines LV1 to LVn are supplied with gray scale voltages for the source line groups every one clock period.
Below the voltage profile of the video lines LV1 to LVn, a clock signal CLK is shown. A control signal S1 outputted from the shift register 21 has a high level voltage during a clock period T1 and a control signal S2 has a high level voltage one clock period later than the control signal S1 i.e. during the next clock period T2. Therefore, the source line group GS1 is in a low impedance state LI, during the period from times t1 to t2, in which it is connected to the video lines LV1 to LVn, whereas the source line group GS2 is in a low impedance state LI, during the period from times t2 to t3, in which it is connected to the video lines LV1 to LVn. Further, the source line group GS3 is in a low impedance state LI, during a period from times t3 to t4, in which it is connected to the video lines LV1 to LVn (not shown in FIG. 2).
In the voltage supplying device 100 shown in FIG. 1, the switch circuit C1 changes from the on-state to the off-state and the switch circuit C2 changes from the off-state to the on-state at time t2. Therefore, the source line group GS1 adjacent to the group GS2 changes from the low impedance state LI to the high impedance state HI, whereas the source lines group GS2 changes from the high impedance state HI to the low impedance state LI. In this case, the source line group GS2 is the low impedance state LI while the source line group GS1 is in the high impedance state HI, so that the supply of the voltage to the source line group GS1 is blocked. Therefore, in the case that the voltage on the source line LS1 of the source line group GS2 changes at the time when the source line group GS2 becomes the low impedance state LI, the voltage on the source line LSn of the source line group GS1 varies due to the cross talk, so that the voltage on the source line LSn of the source line group GS1 deviates from the original voltage. Ditto for the source lines LSn of the other source line groups.
An object of the present invention is to provide a voltage supplying device which can return a voltage on a line to the original voltage when the voltage on the line varies due to the cross talk between adjacent lines.